1. Field of the Invention
The present invention relates to improved cement compositions and novel biodegradable dispersants therefor.
2. Description of the Prior Art
Dispersants are often used in cement compositions utilized in construction for facilitating the mixing of the cement compositions. Also, in the cementing of oil and gas wells and the like, dispersants are extensively used to reduce the apparent viscosities of the cement compositions utilized. The reduction of the apparent viscosity of a cement composition allows the cement composition to be pumped with less friction pressure and utilizing less pump horsepower. In addition, the lower apparent viscosity often allows the cement composition to be pumped in turbulent flow. Turbulent flow characteristics are desirable when pumping cement compositions in oil and gas wells to more efficiently remove drilling fluid from surfaces in the well bore as the drilling fluid is displaced by the cement composition being pumped. The inclusion of dispersants in cement compositions is also desirable in that the presence of the dispersants reduces the water required for preparation of the cement compositions. Cement compositions having reduced water content are characterized by improved compressive strength development.
A number of dispersing agents have been utilized heretofore in cement compositions, particularly in cement compositions used for primary and remedial cementing in oil and gas wells. For example, certain organic acids such as gluconic acid and citric acid have been recognized by those skilled in the art as cement dispersants. However, such organic acids are also strong cement composition set retarding agents which is often undesirable. That is, the presence of an organic acid dispersant in a cement composition prevents the cement composition from setting for a relatively long period of time which is often costly or otherwise detrimental. Other dispersants which are commonly used in hydraulic cement compositions include polynapthalene sulfonate which is commercially available under the trade designation "CFR-2.TM." from Halliburton Energy Services of Duncan, Okla., the condensation product of formaldehyde, acetone and a sulfite which is commercially available under the trade designation "CFR-3.TM." from Halliburton Energy Services, poly-B-naphthol sulfonate, polymelamine sulfonate, and many others. While such dispersants function very well in cement compositions, they are not environmentally acceptable, especially in offshore operations, in that they do not undergo complete biodegradation in the environment and cause damage to aquatic and other life therein.
Thus, there are needs for biodegradable cement composition dispersants and improved cement compositions containing such dispersants.